Spark gap structure with annular concentric magnets for rotating arc



y 6, 1967 c J. KAWIECKI 3,320,462

SPARK GAP STRUC'iURE WITH ANNULAR CONGENTRIC MAGNETS FOR ROTATING ARC Filed Sept. 10, 1963 2 Sheets-Sheet 1 CHESTER JJfAW/ECK/ INVENTO/Z 5r Fig.3 BUCKHORN, BLORE, KLAROU/ST a SPAR/(MAN ArroRA/Em May 16,1967 c. J. KAWIECKI 3,320,462

SPARK GAP STRUCTURE WITH ANNULAR CONCENTRIC MAGNETS FOR ROTATING ARC CHESTER J. KAW/ECK/ By l/VVE/VTOP.

BUG/(HORN, BLORE, KLAROU/ST 8 SPAR/(MAN ATTORNEYS United States Patent Ofifice 3,320,462 Patented May 16, 1967 3,320,462 SPARK GAP STRUCTURE WITH ANNULAR gglgltCENTRIC lMAGNETS FOR ROTATING Chester J. Kawieclri, Chicago, 11]., assignor to Joslyn Mfg. and Supply Co., Chicago, Ill., a corporation of Illinois Filed Sept. 10, 1963, Ser. No. 307,941 9 Claims. (Cl. 313-154) The present invention relates to a lightning or surge arrester and more particularly to a spark gap structure for use in a lightning arrester or like device.

It is frequently necessary to connect communication and like electronic equipment in circuits subject to high voltage surges which if they reached the equipment would damage it. For example, communication equipment in aircraft must be protected from surges resulting from lightning strokes striking the antenna. To protect the communication equipment from damage by the high current surges resulting from lightning discharges various lightning arresters have been developed which function to pass the high current surges to the frame of the aircraft. An example of a prior art structure for this purpose is that shown in Patent 2,906,922. The structure in this patent includes a capacitor in series with the antenna and communication equipment through which the normal RF. signals may pass. Connected to the antenna line leading to such capacitor is a spark gap unit which is grounded to the frame of the aircraft. The spark gap unit is designed to bypass to ground the high current developed from a lightning discharge.

The spark gap unit of Patent 2,906,922 comprises a pair of concentric annular electrodes in the inner one of which is mounted a permanent magnet polarized to provide a field in the gap between the electrodes so that upon the development of an are between the electrodes the arc will be caused to spin around the electrodes thus minimizing the contact time of the are upon the surface of the electrodes at any one point and minimizing the possibility of pitting or scarring of the electrode surface which, if it occurs, may impair or entirely destroy the operability of the arrester to pass the discharges to ground. This arrester functions adequately when the lightning stroke is a negative stroke, that is, of such polarity that upon arcing electrons flow from the inner to the outer electrode. However, it was found that performance was erratic and the are developing between the electrodes would not always spin if the lightning stroke was of positive polarity. In other prior art gap structures utilizing magnets in the spark gap, the high current pulse resulting from a high voltage surge frequently causes demagnetization of the magnets, th-us destroying the capability of the gap.

Accordingly, it is the principal object of the present invention to provide a spark gap unit having a continuous gap with magnetic means associated with said gap to cause the arc to move around the gap regardless of the polarity of the high voltage surge applied to said gap.

More particularly, it is an object of the present invention to provide a spark gap unit embodying concentric annular electrodes wtih magnetic means associated with each electrode to effect movement of an arc developing between the electrodes around the gap and along the surfaces of the electrodes.

Still another object of the present invention is to provide a spark gap unit including concentric annular electrodes each of which has an annular permanent magnet associated therewith for establishing magnetic fields between the electrodes such t-hat any are developing between the electrodes is caused to move along the surfaces thereof and around the gap.

A further object is to provide a lightning arrester ineluding a spark gap structure having a pair of annular electrodes provided with permanent magnets with the electrodes so constructed that currents resulting from high voltage discharges across the gap will not effect depolarization of the magnets.

A still further object of the invention is to provide a spark gap unit of the nature described above utilizing permanent magnets with means associated with such magnets to distribute and provide a uniform field.

Still other objects and advantages of the invention will become more apparent hereinafter.

In accordance with an illustrated embodiment, the present invention comprises a spark gap unit having a pair of concentric annular electrodes spaced from one another so as to define a spark gap therebetween. Mounted in each of the electrodes is a permanent magnet, the magnets in each electrode being polarized in such manner that a magnetic field is provided about each electrode, the fields being substantially independent of one another. Upon development of an are between the electrodes the force of the magnetic field exerted upon the electrons in the arc will cause such are to move around the gap and along the surfaces of the electrodes, regardless of the direction of the current fiow across the gap, so that the arc is not maintained at any point on the electrodes sufficiently long to effect overheating and pitting or scarring of the electrode surfaces.

The invention will now be described in greater detail in connection with the accompanying drawings wherein FIG. 1 is a schematic diagram of a circuit embodying a lightning arrester having a spark gap in accordance with the invention;

FIG. 2 is an elevation partly in section of an arrester construction in accordance with the invention;

FIG. 3 is an enlarged fragmentary view illustrating the spark gap structure in the arrester of FIG. 2;

FIG. 4 is a semi-schematic sectional view of the spark gap illustrating a magnet arrangement and associated field;

FIG. 5 is a view similar to FIG. 4 illustrating another suitable magnet arrangement;

FIG. 6 is an elevation partly in section of a modified arrester construction;

FIG. 7 is an enlarged fragmentary sectional view illustrating the spark gap of the arrester of FIG. 6;

FIG. 8 is a semi-schematicsectional view of the spark gap structure of FIG. 6 illustrating a suitable magnet arrangement and resulting field; and

FIG. 9 is a view similar to FIG. 8 showing another suitable magnet arrangement.

Referring now to the drawings and more particularly to FIG. 1, schematically indicated therein is a lightning arrester 20 having a spark gap constructed in accordance with the invention. The arrester is shown connected between the antenna 22 and communications equipment 24 of an aircraft or other vehicle. The arrester 20 includes a capacitor 26 for passing RF. signals from the antenna to the communications equipment and a resistor 28 connected in parallel with the capacitor to provide a leakage path for static charges accumulating on the antenna 22. Indicated at 30 is the spark gap unit which is connected between the antenna lead 32 and the frame of the vehicle so as to bypass to such frame high current surges resulting from lightining discharges striking the antenna 22.

Referring now more particularly to FIG. 2 a lightning arrester structure provided with a spark gap in accordance with one embodiment of the invention is illustrated as comprising an envelope 36 which is formed of glass or other suitable insulating material. The envelope is shown as comprising a main body portion made up of two, tubular, cup-shaped shell halves 38, 39 and a cap 40 which is formed of metal. A gasket 42 is positioned between the cap and the top of the shell 38. Extending outwardly from and sealed to the cap 40 is a terminal 44 for connection to an antenna lead.

The envelope 36 encloses and protects a surge blocking capacitor structure 5t which may be constructed substantially as shown in Yonkers et al. Patent 2,906,925 or be of other suitable construction. The capacitor St) is supported at one end by a lead-in terminal 52 extending from the antenna terminal 44 inwardly through the cap 413 and supported at its other end by a terminal 54 to which a connection to the transmission equipment 24 may be made. A gasket 55 is positioned between a flange 56 of the terminal 54 .and the end wall of envelope section 39 so as to provide a hermetic seal therebetween.

The outer cylindrical shell of the capacitor St) is formed of metal and constitutes one plate of the capacitor and is connected electrically to the antenna terminal 44. Mounted upon the capacitor body 5% is the inner electrode 60 of a spark gap unit made in accordance with the instant invention. Surrounding the inner electrode 60 is an outer, annular electrode 62 which defines with the inner electrode 60 an endless, annularly extending spark gap 63.

Referring now more particularly to FIG. 3, the inner electrode 60 includes a mounting flange portion which snugly engages the capacitor plate 56 and preferably is brazed or soldered thereto as indicated at 72 so as to provide a good electrical connection between capacitor body 50 and the flange 70. The electrode 69 also includes a body portion 74 having an outwardly facing cylindrical surface 76, the body 74 being supported from the flange 79 by an arm 78. Extending inwardly toward the capacitor 50 from the opposite edge of the electrode body 74 is a stub flange 80 which defines with the arm 78 an annular space in which is mounted an annular permanent magnet 82. The flange 80 is spaced from the capacitor 50 to provide a gap 81 for a purpose to be ex plained. The magnet 82 is axially polarized so as to have annular poles at the top and bottom ends, as the magnet is shown in FIG. 3, and preferably soft iro-n rings 84 are provided adjacent each of the pole faces to assure uniform flux distribution. A washer 86 of a suitable resilient material such as fiber is preferably provided between the lOwer soft iron ring 84 and the flange 80. In assembling the magnet 82 within the electrode 60 the flange 80 is spun or otherwise bent over from a downwardly extending position with respect to the body 74- into snug engagement with the washer 86 after the other units are mounted within the electrode so as snugly to hold the magnet and rings in position.

The outer electrode 62 comprises a body portion 90 defining a cylindrical surface 92 which faces and is concentric with the surface 76 of the inner electrode 60 so that the gap 63 defined by such faces is of substantially equal Width around the entire periphery of the electrodes. 7

The body 90 is also provided with an annular aperture 94 within which is mounted an axially polarized, annular permanent magnet 96. Soft iron rings 98 are provided adjacent each of the poles of the magnet 96 for the purpose of evenly distributing the flux. A resilient washer 100 is positioned between the lower ring 98 and a pair of flanges 102, 104 which extend inwardly from the opposite sides of the electrode defining the aperture 94. Prior to assembly the flanges 102, 164 extend substantially parallel to the side walls of the aperture 94 so as to permit insertion of the magnet 96, rings 98 and washer 100. Thereafter the flanges 102, 104 are spun or otherwise bent over into snug engagement with the washer 100 so as snugly to secure the magnet and rings in position within the aperture. As may be seen in FIG. 3, a gap 105 remains between the ends of the flanges 102, 104 so that current may not flow across the electrode beneath the electrode and the rings 98 likewise are of lesser width than the width of the aperture 94 so as not to provide a circuit across the rings.

The electrode body 96 is supported from the envelope by means of an integral mounting flange 1% which is brazed to a further mounting flange Hi7. The flanges 1%, ltd? extend outwardly between the envelope portions 38, 3@ and washers 66, 63 are provided between the flanges and the envelope portions to form a seal therebetween. The mounting flange M37 is adapted to be suitably secured to supporting structure to mount the arrester in position in the equipment in which it is to be used and is suitably electrically grounded. To protect the capacitor 5% shields 110, 112 of suitable insulat ing material such as Teflon are preferably provided on the capacitor body on opposite sides of the inner electrode 6i Similarly, to protect the envelope portions 38, 3 9 from arcing or sputtering, arcing shields 114, 116 of metal or insulating material are preferably mounted on the outer electrode mounting flanges 186, 187.

In accordance with the present invention the magnets 82, $6 are arranged to produce a magnetic field adjacent each of the electrodes 6%, 62 such that electrons emerging from either electrode are subjected to a force substantially normal to the axis of the electrodes so that such electrons will tend to circle such axis as they traverse the gap 63. To attain such action the pole arrangement of magnets 82, )6 must be such that the fields adjacent each electrode are substantially independent of the other and preferably the magnets are of substantially equal strength so that the fields developed thereby are of substantially equal intensity. One suitable magnet arrangement is shown in FIGS. 3 and 4 wherein the magnets 32, 96 are annularly polarized in the axial direction with the magnets so arranged that the pole arrangement of the magnets are mirror images with respect to each other, that is, the south poles of the magnets are opposite each other and the north poles are opposite each other. Referring to FIG. 4, with such a pole arrangement the magnetic fields about the electrodes are substantially as indicated in dotted lines and as will be seen the field of each magnet is substantially independent of the other because of the mutual interaction between the fields. Each electrode of 62 will thus have a substantially strong magnetic field adjacent the gap face thereof so that any electron emerging from the gap face of either electrode is subjected to a force which tends to move the electron at right angles to the axis of the electrodes and at right angles to a radii of the electrodes. Thus upon occurrence of a high voltage surge, as from a lightning stroke, which causes the breakdown voltage of the gap to be exceeded, the developing are will be caused to spin around the gap between the electrodes regardless of the polarity of the surge. While in the illustrated arrangement the south poles are in the upward position it will be apparent the pole positions can be reversed.

Referring to FIG. 5, a further suitable magnetic arrangement comprises radially polarized magnets 82 and 96 having annular poles, the magnets in this case being arranged so that the adjacent poles are alike. That is, as shown in FIG. 5, the inner magnet 32 may be arranged so that its north pole faces outwardly whereas the outer magnet 96 may be arranged so that its north pole faces inwardly. Alternatively, the opposite arrangement could be utilized, that is, the inner magnet could be arranged so that its south pole faces outwardly and the outer magnet could be arranged so that its south pole faces inwardly towards the inner magnet. In either case, substantially independent magnetic fields will be developed between the electrodes substantially as shown in dotted lines in FIG. 5, and, upon initiation of an arc, irrespective of the direction of current flow between the electrodes the arc will be caused to move around the gap between the electrodes.

The electrodes 64), 62 are preferably formed of a good electrical and heat conductive material such as brass, copper, Wolfram, or molybdenum and are relatively massive so as to provide a heat sink for heat developed during are over. The magnets 82, 16 are preferably of the ceramic type so that they are self insulating and thus resist flow therethrough of the current resulting from a lightning discharge which, if it passed through a magnet would result in demagnetization thereof. To prevent demagnetization of the magnets it is also important to pro vide the gaps 81, 105 and prevent current flow through the hollow core of the magnets, and linking of either magnet annulus which if it occurred would likewise result in demagnetization of the linked magnet. As will be apparent with the gap arrangement shown, all of the current flow is outside of the magnets or about the outer periphery thereof and repeated surges of high current (100,000 amperes or more) may pass through the electrodes without injury to the magnets. It is also desirable to distribute the current flow through the electrodes as evenly as possible since concentration or channelization of flow might result in such high current values and resulting localized fields as to demagnetize the magnet completely or partially or cause a reverse of polarity either entirely or in spots. Any such event would impair the operability of the gap. For this reason, it is important that the electrodes be brazed to their supporting structures as shown.

The arrester may be filled with dry air or with any suitable gaseous dielectric such as sulfur hexafluoride or may be vacuumized. It is preferably hermetically sealed, as shown, so as to maintain uniform conditions within the arrester though ambient conditions may change.

Because the are following a lightning stroke or other high voltage pulse of either negative or positive polarity is moved rapidly around the electrodes, 60, 62, spot overheating of the electrodes is prevented and pitting or scarring is minimized. Thus, the arrester is capable of sustaining and bypassing repeated strokes.

A modified form of the invention is shown in FIGS. 6 to 9, to which reference is now made. The modified arrester comprises an envelope including opposite portions 130, 132 of glass or other suitable insulating material, and a center portion 134 preferably of brass or other suitable electrically conductive material. The portions 131}, 132 are separated from the portion 134 by gaskets 136 so that the envelope may be hermetically sealed. Mounted within the envelope is a resistor-capacitor structure comprising a housing 140. Any suitable capacitor arrangement may be utilized, and details therefor are not shown. The capacitor is electrically connected to a receiver terminal 142 which extends outwardly of the end of the envelope portion 132. The capacitor 140 is also connected to an antenna terminal 144 extending outwardly of the end of the envelope portion 130, the connecting means including a stem 145 which extends upwardly through mounting hardware contained within a housing 148 which also is electrically connected to the antenna terminal 144. Suitable hermetic seals are provided be tween the terminals 142, 144 and corresponding envelope ends.

The spark gap unit of the present embodiment includes a pair of coaxial, annular electrodes 156, 158 which are spaced axially apart and for convenience will hereinafter be referred to as the upper and lower electrode respectively. With particular reference to FIG. 7 the upper electrode 156 comprises a body which is U-shaped in cross section and includes an outer annular wall 159 that is of greater length than an inner annular wall 160, the outer annular wall being threaded or otherwise suitably engaged on the lower end of the housing 148. Preferably, the wall 151 is brazed to the housing 148, as in dicated at 162., so as to provide an efficient electrical connection between the electrode and the housing. Mounted within the hollow center portion of the electrode 156 is an annular, ceramic type, permanent magnet 164 which, in the embodiment shown, is polarized axially with a lower south pole and an upper north pole. Soft iron, flux distributing rings 166 are mounted adjacent both the upper and lower pole faces of the magnet and a washer 168 of suitable resilient material is positioned between the upper ring 166 and the lower end of the housing 148. In mounting the electrode upon the housing 14;; the magnet assembly is inserted within the electrode and the electrode then threaded onto the housing until the washer 168 is compressed snugly against the lower end of the housing 143. The resilience of the washer maintains the magnet assembly in position within the housing. It will be observed that the wall of the electrode is positioned below the lower end of the housing 148 so as to provide a gap 170 whereby electrical current flowing between the housing 148 and the electrode 156 must pass through the wall 159 and around the magnet rather than through the core thereof. The lower end of the electrode 156 is formed as a flat, annular surface 1'72 which faces the upwardly facing fiat surface 174 of the lower electrode 158.

The lower electrode 158 is of inverted U-shape and has mounted between the arms thereof an annular magnet 176 that is polarized axially to provide annular poles thereon, the magnet being mounted with the south pole thereof facing upwardly and the north pole downwardly. Preferably soft iron rings 178 are mounted adjacent each of the pole faces of the magnet 176. In assembly of the electrode 158 the magnet 176 and rings 178 are positioned within the interior of the electrode and flanges 130, 182, which prior to assembly extend downwardly from the opposite walls of the electrode, are then spun or otherwise bent over into the position shown and into snug engagement with a suitable resilient gasket 134, so that, as in the other electrode assemblies described, the magnet 176 and rings 178 are held securely in position within the electrode. The electrode 158 is secured, as by brazing indicated at 186, to an annular flange 188 which extends outwardly of the envelope and provides a means for mounting the arrester within the structure in which it is to be used. Preferably the ring 134 is brazed, as indicated at 190, to the mounting flange 188. It will be observed that the flanges 180, 182 are spaced from one another so as to provide an annular gap 185 therebetween, thus preventing any current flow through the core of the magnet, the flow being restricted to a path from the flange 188 to the surface 174.

In use, the arrester of the present embodiment is connected in the communication circuit in the manner shown in FIG. 1, with the mounting flange 188 connected to the frame of the aircraft or otherwise suitably grounded. Normal RF. signals will flow through the arrester through the capacitor 140 to the receiver terminal 142 and thence to the communications equipment. However, should lightning discharge occur at the antenna of the communications equipment, the capacitor will be charged and upon reaching the breakdown voltage of the gap 175, an arc will develop across the gap and the high current surge from the lightning will be diverted to ground or to the surface of the aircraft. Upon development of the arc the magnetic fields developed by the magnets 164, 176 will cause the arc to rotate about the axis of the electrodes, and such rotation will be caused irrespective of the polarity of the lightning discharge. To protect against the possibility of arc-over to the rod 146, it is preferably provided with an insulating sleeve 190 of Teflon or like material. The ring 134 defines a chamber encircling the gap 175 to confine an are between the electrodes and to protect the envelope portions 131, 132 from the are or any sputtering which may occur.

As shown in FIG. 8, the magnets 164, 176 are arranged with the south poles of the magnets adjacent one another so that a strong field is developed adjacent the face of each electrode with the flux lines extending radially so that an are developing between the electrodes is caused to spin irrespective of the direction of current flow. The magnets may be reversed in their position so that the north i poles of the respective magnets are next adjacent one another.

Still another suitable arrangement of magnets is illustrated in FiG. 9. In this arrangement the electrodes 156, 158' are provided with magnets 2th), 2%, respectively, having radially displaced annular poles, the pole arrangement on the magnets being mirror images with respect to each other. While the magnets are shown in FIG. 9 as having south poles on their inner periphery and north poles on their outer periphery, the pole positions could be reversed. Again, with a magnet arrangement as shown in FIG. 9, an arc developing between the electrodes 156, 158 will spin about the gap between the electrodes irrespective of the direction or" current flow across the gap.

A desirable feature of both embodiments is that the arc caused by the power follow current following a stroke caused surge is automatically extinguished by blow out of the are due to the interaction of the magnet fields and the field of the power follow current.

While the invention has been particularly described in connection with aircraft type lightning arresters, it will be obvious that the spark gap unit of the invention is suitable for use in other types of high voltage protection equipment.

Having illustrated and described preferred embodiments of the invention, it should be apparent to those skilled in the art that the invention permits of modification in arrangement and detail. I claim all such modifications as come within the true spirit and scope of the appended claims.

I claim:

1. In a surge arrester:

a spark gap arrangement comprising a pair of concentric annular electrodes formed of a conductive substantially non-magnetic material;

surge current connector means attached to each of said electrodes,

a pair of annular, annularly polarized permanent type magnets located one within each of said electrodes for providing a magnetic field about each electrode;

said fields being of substantially equal intensity;

said electrodes each having an annular discontinuity therein so positioned with respect to said surge current connection means that surge current passing through said electrode cannot flow through the hollow core of cit-her of said magnets to link said magnets.

2. A surge arrester as in claim 1 wherein said electrodes are axially spaced from one another.

3. A surge arrester as in claim 1 wherein said electrodes are radially spaced from one another.

4. In a surge arrester:

a spark gap arrangement comprising a pair of axially displaced annular concentric electrodes;

surge current connector means attached to each of said electrodes,

a pair of annular permanent magnets mounted one in each of said electrodes in coaxial relation to each other;

said magnets having radially displaced annular poles;

the pole arrangement of said magnets being such that the adjacent poles of said magnets are of like polarity;

said electrodes each having an annular discontinuity therein so positioned Wit-h respect to said surge current connection means that surge current passing through said electrode cannot flow through the hollow core of either of said magnets to link said magnets.

5. In a surge arrester:

a spark gap arrangement comprising a pair of annular,

concentric, axially displaced electrodes;

surge current connector means attached to each of said electrodes,

a pair of annular permanent magnets mounted one in each of said electrodes in coaxial relation to each other;

said magnets having axially displaced annular poles;

the pole arrangement on said magnets being such that the adjacent poles of said magnets are of like polar- W;

said electrodes each having an annular discontinuity therein so positioned with respect to said surge current connection means that surge current passing through said electrode cannot flow through the hollow core of either of said magnets to link said magnets.

6. A spark gap arrangement, comprising:

a pair of annular concentric electrodes of substantially the same inner and outer diameters spaced axially from one another and defining facing, generally radially extending annular surfaces between which arcing may occur;

surge current connect-or means attached to each of said electrodes,

a pair of annular permanent magnets of substantially the same inner and outer diameters mounted one in 7 each of said electrodes;

said magnets being polarized radially and identically;

said electrodes substantially enclosing said magnets but each having an annular gap so arranged therein with respect to said surge current connector means as to provide an open circuit through the core of the respective magnet whereby no current flow through the core of the magnets will occur upon are over between said electrode surfaces.

7. A spark gap arrangement comprising:

a pair of annular concentric electrodes of substantially the same inner and outer diameters spaced axially from one another and defining facing, generally radially extending annular surfaces between which arcing may occur;

surge current connector means attached to each of said electrodes,

a pair of annular permanent magnets of substantially the same inner and outer diameters mounted one in each of said electrodes;

said magnets being polarized axially;

the next adjacent poles of said magnets being of the same polarity;

said electrodes substantially enclosing said magnets but each having an annular gap so arranged therein with respect to said surge current connector means as to provide an open circuit through the core of the respective magnet whereby no current flow through the core of the magnets will occur upon arc-over between said electrode surfaces.

8. In a surge arrester:

a spark gap arrangement comprising a pair of concentric annular electrodes;

an annular permanent magnet mounted in one of said electrodes and polarized to produce a magnet field therein to cause an arc developed between the electrodes to move around the gap between said electrodes;

surge current connection means attached to said one of said electrodes;

said one electrode having an annular discontinuity therein so positioned with respect to said surge current connection means that surge current passing through said electrode from the other electrode cannot flow through the hollow core of said annular magnet to link said magnet, said discontinuity breaking the surge current path from said connection means to said gap through the hollow core of said annular magnet.

9- A lightning or surge arrester of the combined spark gap capacitor type comprising:

an elongate insulated housing;

a pair of terminals one at each of the opposite ends of said housing, including an antenna terminal and an output terminal;

a capacitor unit supported in said housing between said terminals;

a first annular electrode mounted in said housing and electrically connected to said antenna terminals;

a first annularly polarized permanent magnet mounted in said first electrode;

a second annular electrode mounted in said housing and defining with said first electrode an annular spark gap;

a second annularly polarized permanent magnet mounted in said second electrode;

said electrodes each comprising a relatively massive body of electrically conductive material substantially surrounding the respective one of said magnets but being formed With an annular gap so as to provide an open electrical circuit through the core thereof;

each of said magnets being polarized in such manner that the fields thereof are substantially independent of one another and upon initiation of an arc between 10 said electrodes the arc is caused to move along both said electrodes irrespective of the direction of current flow between the electrodes; and means connected to said second electrode and extending outwardly of said housing for connecting said second electrode to ground.

References Cited by the Examiner UNITED STATES PATENTS 1,733,679 10/1929 Toulon "315-144 2,031,435 2/1936 Thompson 313-154 2,862,132 11/1958 Dyer 313-156 2,906,922 9/1959 Huber 315-59 2,906,925 9/ 1959 Yonkers et al. 313-324 2,926,276 2/1960 Moriya et al 313-153 2,985,788 5/1961 Opsahl et al 313-153 3,047,769 7/1962 Hicks et :al. 315-36 3,254,268 5/1966 Radus et al. 313-156 20 JAMES W. LAWRENCE, Primary Examiner.

ROBERT SEGAL, Examiner. 

1. IN A SURGE ARRESTER: A SPARK GAP ARRANGEMENT COMPRISING A PAIR OF CONCENTRIC ANNULAR ELECTRODES FORMED OF A CONDUCTIVE SUBSTANTIALLY NON-MAGNETIC MATERIAL; SURGE CURRENT CONNECTOR MEANS ATTACHED TO EACH OF SAID ELECTRODES, A PAIR OF ANNULAR, ANNULARLY POLARIZED PERMANENT TYPE MAGNETS LOCATED ONE WITHIN EACH OF SAID ELECTRODES FOR PROVIDING A MAGNETIC FIELD ABOUT EACH ELECTRODE; SAID FIELDS BEING OF SUBSTANTIALLY EQUAL INTENSITY; 